There are rules for a Cleric who loses faith, and how to regain his standing through atonement.

But what if he abandons one faith entirely for another? Presumably his new god/faith should be picking up where the other leaves off, so spells aren’t interrupted, and further he probably should be changing his Domains to ones used by his new faith, but does any official book actually describe this process? Does his new faith require atonement for his prior faith in another religion? Is there some kind of interruption time period, where he doesn’t get spells? Is the actual process of substituting Domains explained?

Because the lack of rules that I’m looking at almost seems to imply that a Cleric cannot change faiths.

I’m really looking for book citations here, because this is specifically for the sake of determining what the rules currently are to better judge how changes might affect them. I have plenty of my own ideas about how this sort of thing should be handled, most of which rely on eliminating as much of alignment’s mechanical impact as possible, but that’s not really relevant here.

If your answer is that there are no such rules, I’d like an idea of how certain you are of this. For example, I could not find any such rules in Player’s Handbook or Complete Divine, the first two places I looked. Knowing where the rules aren’t is useful.

+1 because it wont let me +2...Ive wondered about the same thing. Hopefully you get some good answers here
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Ben-JaminJan 15 '13 at 14:31

2

I've seen this happening a campaign, and the GM houseruled the outcome based purely on the agenda of the cleric's new god and that god's relationship with the ones the cleric used to follow. It was pretty circumstantial and campaign-specific - Which is my point: It might be best to handle this on a case-by-case basis.
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GMJoeApr 8 '13 at 5:55

@GMJoe In all honesty, I have absolutely no intention of ever following these rules (because I hate the falling mechanics in the first place), I just wanted to know what they are so I can come to an informed decision about how to change them.
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KRyanJul 5 '13 at 15:35

3 Answers
3

This is a sidebar at the bottom of the referenced page, which is part of a section on rules for retraining. If you don't have the book, here is the direct quote:

DIVINE CONVERSION

As noted in the Player’s Handbook, a cleric who grossly violates the
code of conduct imposed by his deity loses all spells and class
features and cannot attain any more levels as a cleric of that deity.
All these penalties remain in effect until he atones. But what if he
doesn’t want to atone? What if a cleric of Hextor finds new meaning
and purpose in serving Heironeous after a dramatic conversion
experience? Such a character need not become a multiclass ex-cleric of
Hextor/cleric of Heironeous. Instead, Heironeous can simply reinstate
the character’s cleric powers once he has proven his loyalty, talent,
and ability.

A cleric who changes his patron deity must complete a quest to prove
his devotion to his new patron. The nature of the quest depends on the
deity, and it always clearly reflects the deity’s alignment as well as
his or her goals and beliefs. To start the process, the cleric must
voluntarily accept a geas/quest spell cast by a higher-level cleric
of his new deity. During the quest, the cleric has no access to spells
or cleric class features—except his weapon and armor proficiencies,
which he does not forfeit.

Upon completing the quest, the cleric receives the benefit of an
atonement spell from a cleric of the new deity. The character then becomes a cleric of the new deity and is inducted into the clergy
during an appropriate ceremony of the DM’s choosing. After selecting
two of the new deity’s domains in lieu of his old ones, the character
has all the powers and abilities of his previous cleric level, plus
the granted powers of his new domains.

This method is the only one by which a cleric can change his deity.
The retraining rules can’t be used to accomplish this task—it is
simply too substantial a change in the character’s identity (not to
mention his source of power) to chalk up to a bit of practice in his
off hours.

This answer essentially reflects the ruling already found in the Forgotten Realms Campaign Setting, but it may be useful to know it's also located in a setting-independent rulebook, just in case there are any sticklers out there.

There is no such rule in the setting-independent supplements that I know.

But setting-specific supplements are another story.

Forgotten Realms Campaign Setting, p233 or something:

Changing Deities

It is possible for a cleric, druid, paladin, or spellcasting ranger (or any other divine spellcaster) to abandon his chosen deity and take up the
faith of another deity. In doing so, the divine spellcaster loses all
class features of the abandoned deity. To progress as a divine spellcaster of another faith, the character must go on a quest for his new
church (often the recovery of a lost item of some importance to the
deity), then receive an atonement spell from a representative of his
new faith. Once these two conditions are met,the character becomes
a divine spellcaster of the new deity, and if a cleric,he chooses two
domains from the new deity's repertoire. The character then
resumes the class features lost from leaving the old faith(so long as
they are still applicable — turning or rebuking undead ability might
change, for instance)

While not worded ideally, these rules implement a simple idea: the same atonement spell does the job.

Perfect! The book might be setting specific, but the rule doesn't really seem to be. Thanks.
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KRyanJan 15 '13 at 16:14

2

+1 This is essentially the same thing I found in PH2, and this rule actually has greater clarification by acknowledging divine spellcasters beyond just the clerics might need conversion through atonement.
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Gargonn BlackmaneJul 5 '13 at 5:00

There is another way that isn't mentioned in any of the other posts. A deity could literally just take on the role of patron of a deity, especially if it isn't a big leap in portfolios. There is an example of this is Exemplars of Evil (Calis Archwinter)